Is one halachically allowed to attend the marriage of a parent?
For example my mother passed away many years ago, and my father
is now remarrying. I've heard that it is not permissible for the
children to attend the wedding, is there any basis for this?

PS If you could reply ASAP I would appreciate it, the wedding
is next Sunday.

Dear David Bitton,

Yes, there is a basis for this. According to widespread custom,
children do not attend a parent's second marriage. One logical
explanation is that the children's presence is a reminder of the
first spouse, and could thus mar the joy of the occasion.

I asked Rabbi Yosef Shalom Elyashiv, shlita, about this
custom. He gave the following explanation: Children have
an obligation to respect their parents even after the parents
have passed away. Attending the marriage of a surviving parent
would be disrespectful to the deceased parent.